A novel optical imaging method that makes use of surface plasmon microscopy (SPM) and phase shift interferometry is developed. It is named phase shift interferometry-surface plasmon microscopy (PSI-SPM). In comparison with SPM, it can measure not only the intensity of the light reflected under SPR conditions, but also the phase of the light. The images of higher resolution (compared with SPM) can be obtained through the synthesis of the phase (color) and intensity (brightness) information.